package com.smit.utils;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * HMac MD5
 */
public final class HMacMD5 {

    private HMacMD5() { }
    /**
     * 计算参数的md5信息
     *
     * @param str 待处理的字节数组
     * @return md5摘要信息
     * @throws NoSuchAlgorithmException 异常
     */
    private static byte[] md5(byte[] str) throws NoSuchAlgorithmException {
        MessageDigest md = MessageDigest.getInstance("MD5");
        md.update(str);
        return md.digest();
    }

    /**
     * @param key  密钥
     * @param data 待加密数据
     * @return 加密结果
     * @throws NoSuchAlgorithmException 异常
     */
    public static byte[] getHmacMd5Bytes(byte[] key, byte[] data) throws NoSuchAlgorithmException {
        /*
         * HmacMd5 calculation formula: H(K XOR opad, H(K XOR ipad, text))
         * HmacMd5 计算公式：H(K XOR opad, H(K XOR ipad, text))
         * H代表hash算法，本类中使用MD5算法，K代表密钥，text代表要加密的数据 ipad为0x36，opad为0x5C。
         */
        int length = 64;
        byte[] ipad = new byte[length];
        byte[] opad = new byte[length];
        for (int i = 0; i < 64; i++) {
            ipad[i] = 0x36;
            opad[i] = 0x5C;
        }
        byte[] actualKey = key; //Actual key. 
        byte[] keyArr = new byte[length]; //Key bytes of 64 bytes length 
        /*
         * If key's length is longer than 64,then use hash to digest it and use
         * the result as actual key. 如果密钥长度，大于64字节，就使用哈希算法，计算其摘要，作为真正的密钥。
         */
        if (key.length > length) {
            actualKey = md5(key);
        }
        for (int i = 0; i < actualKey.length; i++) {
            keyArr[i] = actualKey[i];
        }

        if (actualKey.length < length) {
            for (int i = actualKey.length; i < keyArr.length; i++) {
                keyArr[i] = 0x00;
            }
        }

        byte[] kIpadXorResult = new byte[length];
        for (int i = 0; i < length; i++) {
            kIpadXorResult[i] = (byte) (keyArr[i] ^ ipad[i]);
        }

        byte[] firstAppendResult = new byte[kIpadXorResult.length + data.length];
        for (int i = 0; i < kIpadXorResult.length; i++) {
            firstAppendResult[i] = kIpadXorResult[i];
        }
        for (int i = 0; i < data.length; i++) {
            firstAppendResult[i + keyArr.length] = data[i];
        }

        byte[] firstHashResult = md5(firstAppendResult);

        byte[] kOpadXorResult = new byte[length];
        for (int i = 0; i < length; i++) {
            kOpadXorResult[i] = (byte) (keyArr[i] ^ opad[i]);
        }

        byte[] secondAppendResult = new byte[kOpadXorResult.length + firstHashResult.length];
        for (int i = 0; i < kOpadXorResult.length; i++) {
            secondAppendResult[i] = kOpadXorResult[i];
        }
        for (int i = 0; i < firstHashResult.length; i++) {
            secondAppendResult[i + keyArr.length] = firstHashResult[i];
        }

        /*
         * H(K XOR opad, H(K XOR ipad, text)) 对上面的数据进行哈希运算。
         */
        byte[] hmacMd5Bytes = md5(secondAppendResult);
        return hmacMd5Bytes;
    }

    /**
     * 获取HMac MD5
     * @param key 密钥
     * @param data 待加密数据
     * @return 加密结果
     */
    public static String getHmacMd5Str(String key, String data) {
        String result;
        try {
            byte[] keyByte = key.getBytes("UTF-8");
            byte[] dataByte = data.getBytes("UTF-8");
            byte[] hmacMd5Byte = getHmacMd5Bytes(keyByte, dataByte);
            StringBuffer md5StrBuff = new StringBuffer();
            for (int i = 0; i < hmacMd5Byte.length; i++) {
                if (Integer.toHexString(0xFF & hmacMd5Byte[i]).length() == 1) {
                    md5StrBuff.append('0').append(Integer.toHexString(0xFF & hmacMd5Byte[i]));
                } else {
                    md5StrBuff.append(Integer.toHexString(0xFF & hmacMd5Byte[i]));
                }
            }
            result = md5StrBuff.toString().toUpperCase();

        } catch (Exception e) {
            return "";
        }
        return result;
    }
}